The arrangement of a throttle in the region of the melt channel at the outlet of a screw extruder is generally known, in order to achieve a pressure buildup in the extruder. Several structural types of throttles are known to constrict or to expand the cross-sectional area of the melt channel. Most throttles are relatively complicated technically and consist of several individual parts as, for example, shown in DE-AS 12 12 295.
A simple structural type consists of a plunger which can be shifted transversely relative to the flow of the melt as disclosed in G. Schenkel, Kunststoff-Extrudertechnik, p. 261, FIG. 6/54. A disadvantage of this construction is that the mass flow of the plastic melt is divided and flow "shadows" arise directly behind the plunger, so that parts of the molten plastic are deposited hereat and then may burn off or decompose.